Nitrogen-containing Ligands Research Articles

Strong enhancement of ionic luminescence Dy(III), Tb(III), Eu(III) and Sm(III) by pyridyltriazoles

With the aim of finding new nitrogen-containing ligands capable of sensitizing the luminescence of lanthanide ion, we synthesized and characterized a series of Tb(III), Eu(III), Gd(III), Sm(III) and Dy(III) complexes with triazole-based ligands. The pyridyltriazole ligands sensitizes very efficiently both the visible emission of the lanthanides, with unusually high luminescence quantum yields in solid state (up to 97% for Tb, 82% for Eu, and 23% for Dy). The results show that the pyridyltriazole ligand provides a very attractive alternative to the classic diketonates and heterocyclic ligands.

Methyl Esters as Cross-Coupling Electrophiles: Direct Synthesis of Amide Bonds

Amide bond formation and transition metal-catalyzed cross-coupling are two of the most frequently used chemical reactions in organic synthesis. Recently, an overlap between these two reaction families was identified when Pd and Ni catalysts were demonstrated to cleave the strong C–O bond present in esters via oxidative addition. When simple methyl and ethyl esters are used, this transformation provides a powerful alternative to classical amide bond formations, which commonly feature stoichiometric activating agents. Thus far, few redox-active catalysts have been demonstrated to activate the C(acyl)–O bond of alkyl esters, which makes it difficult to perform informed screening when a challenging reaction needs optimization. We demonstrate that Ni catalysts bearing diverse NHC, phosphine, and nitrogen-containing ligands can all be used to activate methyl esters and enable their use in direct amide bond formation.

A Remarkable Effect of Aluminum on the Novel and Efficient Aqueous-Phase Hydrogenation of Levulinic Acid into γ-Valerolactone Using Water-Soluble Platinum Catalysts Modified with Nitrogen-Containing Ligands

The catalytic performance of novel water-soluble platinum catalysts modified with various nitrogen-containing and phosphine ligands in the hydrogenation reaction of levulinic acid (LA) into γ-valerolactone (GVL) has been studied in environmentally attractive, green, aqueous monophasic systems. The presence of the Lewis acid aluminum enormously increases the catalytic activity of water-soluble platinum catalysts modified with nitrogen-containing ligands in the LA hydrogenation reaction and high catalytic activities up to 3540 TOF’s per hour with a quantitative selectivity towards GVL have been achieved using Na2PtCl6·6H2O precursors modified with the bidentate bathophenanthrolinedisulfonic acid disodium salt (BPhDS) ligand and low amounts of AlCl3·6H2O promotors (molar ratio of AlCl3·6H2O/Pt = 0.17) in aqueous media. This unprecedented increase in catalytic activity with aluminum promotors for water-soluble transition metal catalytic systems in aqueous-phase hydrogenation reactions has not been described until now in the literature. The apparent activation energy of platinum catalyst modified with the monodentate nitrilotriacetic acid trisodium salt ligand in aqueous medium was calculated and amounts to a relative low value of 73.04 kJ mol−1 when one considers that in the LA hydrogenation reaction this catalyst reduces a less reactive keto group into alcohol functionality. A recycling experiment of the Pt/BPhDS/Al catalyst from the aqueous monophasic LA hydrogenation reaction mixture followed by biphasic recovery of the catalyst in active form from organic reaction products by extraction and simple phase separation of an aqueous/organic two-phase system formed after addition of diethyl ether has shown that the Pt/BPhDS/Al catalyst is stable without loss of activity and selectivity in a consecutive run.

Hydrolytically Stable Nanotubular Cationic Metal-Organic Framework for Rapid and Efficient Removal of Toxic Oxo-Anions and Dyes from Water.

Cationic framework materials capable of removing anionic pollutants from wastewater are highly desirable but relatively rarely reported. Herein, a cationic MOF (SCNU-Z1-Cl) possessing tubular channels with diameter of 1.5 nm based on Ni(II) and a nitrogen-containing ligand has been synthesized and applied to capture hazardous anionic contaminants from water. The SCNU-Z1-Cl exhibits high BET surface area of 1636 m2/g, and shows high hydrolytically stability in pH range from 4 to 10. Owing to the large tubular channels and the uncoordinated anions in the framework, the aqueous-phase anion-exchange applications of SCNU-Z1-Cl were explored with environmentally toxic oxo-anions including CrO42-, Cr2O72-, MnO4-, and ReO4-, and organic dyes. The adsorption of oxoanions exhibits high uptake kinetics and the adsorption capacities of CrO42-, Cr2O72-, MnO4-, and ReO4- are 126, 241, 292, and 318 mg/g, respectively, which were some of the highest values in the field of MOF/COF. In additional, the selectively is high when other concurrent anions are exist. The anionic dyes with different sizes including methyl orange, acid orange A, congo red, as well as methyl blue can be adsorbed by SCNU-Z1-Cl in few minutes to about 1 h. The adsorption capacities for them are 285, 180, 585, and 262 mg/g, respectively. In contrast, the adsorption kinetics for catinionic dyes with different sizes is obviously lower and exhibit a size-selectively adsorption that only cationic dye with suitable size (rhodamine B) can be adsorbed by SCNU-Z1-Cl. Consequently, SCNU-Z1-Cl can sepearate organic dyes in three different modes: size-dependent, charge-dependent, and kinetics-dependent selective adsorption. The excellent adsorption and separation properties of SCNU-Z1-Cl is attribute to the cationic framework, large tubular channel, as well as the high positive Zeta potential.

Complexation and exopolyhedral substitution of the terminal hydrogen atoms in the decahydro-closo-decaborate anion in the presence of cobalt(II)

Reactions between the decahydro-closo-decaborate anion and nitrogen-containing organic ligands L (2,2′-bipyridine (Bipy), 2,2′-bipyridylamine (BPA), phenanthridine (5NPhen)) in the presence of the cobalt(II) ions have been found to give either the corresponding cobalt(II) complexes or the substituted derivatives of the boron cluster depending on the reaction conditions (temperature, solvent (CH3CN or DMF), air/inert atmosphere, and the reagent ratio). It was found that the mono-substituted derivative [2-B10H9OC(H)O]2− with the corresponding residue of the DMF molecule as the substituent can be obtained in the presence of cobalt(II) by the reaction between CoCl2, [B10H10]2−, and DMF whereas cobalt(II) complexes with Bipy, BPA and 5NPhen have been prepared in the presence of the corresponding ligands. In addition, the whole DMF residue, the –OC(H)N(CH3)2 function, can be introduced in the boron cluster by the acid-catalyzed nucleophilic substitution when [B10H11]− was heated in DMF. Crystals of compounds [Co(Phen)3][2-B10H9OC(H)O]·3DMF (Phen is 1,10-phenanthroline additionally introduced into the reaction solution), (Et3NH)[2-B10H9-OC(H)N(CH3)2], [Co(BPA)2(DMF)2][B10H10]·C6H6, [Co(Bipy)3][B10H10], and [Co(5NPhen)2Cl2] were characterized by single crystal X-ray diffraction. Both the substituted derivatives of the boron cluster synthesized here contain exopolyhedral B–O bonds.

Design strategies for the development of a Pd-based acetylene hydrochlorination catalyst: improvement of catalyst stability by nitrogen-containing ligands.

Acetylene hydrochlorination is an attractive chemical reaction for the manufacture of polyvinyl chloride (PVC), and the development efforts are focused on the search for non-mercury catalyst systems. Supported Pd-based catalysts have relatively high activity in the catalytic hydrochlorination of acetylene but are still deactivated rather quickly. Herein, we demonstrated that the atomically dispersed (NH4)2PdCl4 complex, distributed on activated carbon, enabled the highly active and stable production of the vinyl chloride monomer (VCM) through acetylene hydrochlorination under low temperature conditions. We found that the presence of nitrogen-containing ligands in the structure of the active center could remarkably improve the stability of the Pd-based catalysts when compared with the case of the conventional PdCl2 catalyst. Further analyses via X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) show that the variations in the Pd dispersion, chemical state and reduction property are caused by the nitrogen-containing ligands. Temperature-programmed desorption (TPD) characterizations illustrated that the N-containing ligands over the (NH4)2PdCl4/AC catalyst might enhance the adsorption of HCl. These findings suggest that in addition to strategies that target the doping modification of support materials, optimization of the structure of the active center complexes provides a new path for the design of highly active and stable Pd-based catalysts.

Хиральные комплексы переходных металлов с хелатными азотными лигандами в асимметрическом гидрировании с переносом водорода

The reaction of catalytic hydrogenation involving hydrogen transfer through unsaturated C = C and C = O bonds in organic compounds in the presence of optically active soluble complexes of transition metals with nitrogen-containing multidentate ligands has recently gained increased popularity. This review is aimed at generalising available information on the most effective and promising metal complex catalysts for asymmetric hydrogenation involving hydrogen transfer, which have been proposed in the past 10–15 years. Since the activity and selectivity of catalysts based on transition metal complexes are largely dependent on their composition and structure, the design of ligands, the presence or absence of stereogenic centres, the stability and configuration of the chelating ligand system, the nature of the dentate atoms present therein are extremely important. Researchers worldwide have been largely focused on the synthesis and use such ligands, as optically active diamines and aminoalcohols with sp3 -hybridized dentate atoms. These compositions are not oxidized in the coordination sphere of transition metals compared to phosphine ligands, at the same time as maintaining a high level of stereogenicity. Optically active ligands with sp2 nitrogen atoms containing the C = N azomethine bond and oxazoline fragments have been considered as a separate group. In complexes with transition metals, these ligands exhibit a high stability in the catalytic hydrogenation reaction with hydrogen transfer. The stereoselectivity of catalysts in some cases increases with an increase in the denticity of nitrogen-containing ligands. Among them are N-heterocyclic N, H, C–ligands in the Rh (III) complexes; Ru (II) complexes with tridentate N, N, N–ligands with chiral oxazoline fragments; C, N, N–ruthenium complexes. In this review, we grouped catalysts by ligand denticity (from 2 to 6). Comparative data on the activity of various catalysts and the stereoselectivity of respective reactions is provided. The effect of the structure of chiral ligands on the catalytic characteristics of metal complexes is discussed. The authors declare no conflict of interests regarding the publication of this article.

Structural tuning of zinc-porphyrin frameworks via auxiliary nitrogen-containing ligands towards selective adsorption of cationic dyes.

Three metal-organic frameworks have been synthesized by using N-containing ligands and meso-tetra(4-carboxyphenyl)porphyrin, which all exhibit distinct selective adsorption capacities toward various organic dyes, illustrating the most important influence of the structural tuning.

Mechanism and origins of ligand-controlled Pd(ii)-catalyzed regiodivergent carbonylation of alkynes.

Transition-metal-catalyzed carbonylation provides a useful approach to synthesize carbonyl-containing compounds and their derivatives. Controlling the regio-, chemo-, and stereoselectivity remains a significant challenge and is the key to the success of transformation. In the present study, we explored the mechanism and origins of the ligand-controlled regiodivergent carbonylation of alkynes with competitive nucleophilic amino and hydroxy groups by density functional theory (DFT) calculations. The proposed mechanism involves O(N)-cyclization, CO insertion, N-H(O-H) cleavage, C-N(C-O) reductive elimination and regeneration of the catalyst. The chemoselectivity is determined by cyclization. Instead of the originally proposed switch of competitive coordination sites, a new type of concerted deprotonation/cyclization model was proposed to rationalize the ligand-tuned chemoselectivity. The electron-deficient nitrogen-containing ligand promotes the flow of electrons during cyclization, and so it favors the O-cyclization/N-carbonylation pathway. However, sterically bulky and electron-rich phosphine controls the selectivity by a combination of electronic and steric effects. The improved mechanistic understanding will enable further design of selective transition-metal-catalyzed carbonylation.

Metal–organic frameworks with 5,5′-(1,4-xylylenediamino) diisophthalic acid and various nitrogen-containing ligands for selectively sensing Fe(iii)/Cr(vi) and nitroaromatic compounds

Four Zn(ii) complexes are applied in selectively sensing Fe(iii)/Cr(vi) and nitroaromatic compounds.

Synthesis and properties of interspersed structure complexes prepared from 4,4'-(phenylazanediyl)- dibenzoic acid with rigid and semi-rigid nitrogen-containing ligands

Three novel coordination polymers (CPs), namely, [CdL (bif)]·H2O (1), [Cd2L2 (tipa)2]·3H2O (2) and [Co2L2 (bif)2]·4DMF (3), (H2L = 4,4'-(phenylazanediyl)dibenzoic acid, tipa = Tris [4-(imidazol-1yl)- phenyl] amine, bif = 2,7-bis(1-imidazoly) fluorene), have been synthesized under hydrothermal conditions withdifferent solvents. Compounds 1–3 were also characterized by FT-IR spectroscopy, elemental analyses, thermal analysis, power X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 displays a 3-fold interpenetrating 3D framework and contains two kinds 1D helical chains, one is the intertwined one-dimensional double helix chain and another is a 5-fold interpenetrating helical chains. Compound 2 shows a 2-fold interpenetrating 3D framework. Compound 3 exhibits a 3-fold interpenetrating 2D layer. Furthermore, complex 2 can be used as a fluorescent probe for detecting Fe3+ ions, and complex 3 shows a good electrochemical reversibility.

Five 3D lanthanide-based coordination polymers with 3,3,6T13 topology: Structures and luminescent sensor for Hg2+ and Pb2+ ions

A series of isostructural lanthanide coordination polymers Ln-CPs, {[Ln2(PBA)3(H2O)3]·DMF·3H2O}n(Ln = La 1, Nd 2, Sm 3, Eu 4, Dy 5), based on a tripodal nitrogen-containing carboxylic ligand (H2PBA=5-(4-pyridin-3-yl-benzoylamino)-isophthalic acid), have been successfully synthesized under solvothermal conditions. Structural analyses show that compounds 1–5 are isomorphous and crystallize in triclinic space group Pī, and feature an interesting 3,3,6T13 network topology with point symbol (4·52)2(42.52.10·6·72)(58.64.10·6·72). There exist two kinds of 1D metal-carboxylate chains, which are further extended into 3D framework through the connection of PBA2- ligands. Moreover, luminescent spectra of compound 4 are also investigated in visible region, which indicates that it could be used to detect toxic metal cations with relatively high sensitivity and selectivity towards Hg2+ and Pb2+ in DMF solvent.

Preferential CO oxidation over CuO[sbnd]CeO2 catalyst synthesized from MOF with nitrogen-containing ligand as precursor

A set of highly dispersed copper ceria catalysts were synthesized by using the CeMOF precursor featured rich nitrogen-containing ligand. Owing to the existence of coordination interactions between metal ions and nitrogen atoms, the copper ions could be adsorbed into the pore of Ce-MOF and stabilized by the ordered nitrogen atom on the pore wall. After calcinations, the generated CuO/CeO2 catalyst featured more well-dispersed active sites, which was evidenced by varieties of characterizations such as FT-IR, UV-vis spectroscopy, PXRD, TEM, H2-TPR, Raman spectroscopy and XPS. The as-synthesized CuO/CeO2 catalysts displayed outstanding catalytic activities and stabilities for preferential carbon monoxide oxidation in H2-rich stream.

Synthesis, characterization and electrochemical properties of two metal cobalt complexes constructed by tetradentate carboxylic

Two new three-dimensional coordination polymers (CPs), [Co(H2L2−) (bibp)]·2H2O (1) and [Co2(L4−) (bib)2]·8H2O (2) (bib = 1,4-diimidazolyl butane, bibp = 4,4′-diimidazolylbiphenyl) have been solvo-/hydrothermal prepared based on tetradentate ligand 5,5-(pentane-1,4-diylbis (oxy))diisophthalic acid (H4L). In CP 1, two chains was formed by Co(II) ion with ligands H2L2− and bibp, respectively, then two chains form into a 2D layer through Co(II) ion. The same two 2D layers constitute a AB layer by inverted manner, then a 3D framework was obtained through the combination of AB layer by π-π stacking. In CP 2, Co (II) atoms are connected by neighboring carboxylic acid ligands L4− to generate 2D layer, then being further connected with nitrogen-containing ligand bib, the 2D layer form a 3D supramolecular network through Co(II) ions. In addition, the electrochemical behaviors of complexes 1 and 2 have been reported.

NH3⋅H2O: The Simplest Nitrogen-Containing Ligand for Selective Aerobic Alcohol Oxidation to Aldehydes or Nitriles in Neat Water.

Aqueous ammonia (NH3⋅H2O) has been shown to serve as the simplest nitrogen‐containing ligand to effectively promote copper‐catalyzed selective alcohol oxidation under air in water. A series of alcohols with varying electronic and steric properties were selectively oxidized to aldehydes with up to 95 % yield. Notably, by increasing the amount of aqueous ammonia in neat water, the exclusive formation of aryl nitriles was also accomplished with good‐to‐excellent yields. Additionally, the catalytic system exhibits a high level of functional group tolerance with −OH, −NO2, esters, and heteroaryl groups all being amenable to the reaction conditions. This one‐pot and green oxidation protocol provides an important synthetic route for the selective preparation of either aldehydes or nitriles from commercially available alcohols.

Effects of Coordination Ability of Nitrogen-Containing Carboxylic Acid Ligands on Nieuwland Catalyst

This article investigated the effect of three nitrogen-containing carboxylic acid ligands for the Nieuwland catalyst system. The catalyst system containing 4.5% N-(2-acetamido) iminodiacetic acid exhibited improved catalytic activity with excellent performance. The yield of monovinylacetylene (MVA) was maintained at 36.7% after 24 h, which was increased by 17.1% relative to the Nieuwland catalyst system. Based on a variety of analyses on the crystals precipitated from the catalyst solutions, it can be inferred that the outstanding performance and lifetime of the catalysts were related to the abilities of these ligands to form strong coordination with Cu+ ions and stabilize them.

Preparation of metal-organic framework-derived porous carbon and study of its supercapacitive performance

Metal-organic frameworks are formed via the connection of transition metals with oxygen- or nitrogen-containing organic ligands; the organic ligands are rich in carbon and contain heteroatoms such as N and P. Herein, NMFC-T porous carbon was prepared with (Ni3(BTC)2(Me2NH)3) as the carbon precursor using the strategy of pre-carbonization and KOH activation. Influence of carbonization temperature on properties of NMFC-T porous carbon was investigated, and the electrochemical performance of NMFC-800 porous carbon was studied using a three-electrode system. Results revealed that NMFC-800 porous carbon has a high specific surface area of 1143 m2g-1 with a mesopore proportion over 80%. Using KOH solution as an electrolyte, the specific capacitance was as high as 211 F g−1 at a current density of 1 A g−1, and the capacitance retention was 81.04% after 5000 cycles. NMFC-800 porous carbon has excellent supercapacitive performance and good cycle stability.

Novel aqueous-phase hydrogenation reaction of the key biorefinery platform chemical levulinic acid into γ-valerolactone employing highly active, selective and stable water-soluble ruthenium catalysts modified with nitrogen-containing ligands

High catalytic activities (TOF = 3000 h−1) have been achieved by novel water-soluble ruthenium catalysts modified with nitrogen-containing ligands such as the bathophenanthrolinedisulfonic acid disodium salt (BPhDS) in the hydrogenation reaction of the renewable polar platform chemical levulinic acid (LA) which possesses a central relevance in the development of biorefineries of the future in a sustainable way to produce with essentially quantitative selectivity of 99.9 mol% γ-valerolactone (GVL) in aqueous media. The apparent activation energy of the Ru/BPhDS catalyst was calculated and amounts a relative low value of 53.3 kJ/mol when one considers that in the LA hydrogenation reaction this catalyst reduces a less reactive keto group into alcohol functionality. A recycling experiment of the Ru/BPhDS catalyst by extraction after addition of diethyl ether has shown that the catalyst is stable without loss of activity and selectivity in a consecutive run.

Syntheses and characterization of α-Keggin- and α2-Dawson-type diplatinum(II)-coordinated polyoxotungstates: Effects of skeletal structure, internal element, and nitrogen-containing ligand coordinated to the platinum center for hydrogen production from water under light irradiation

The tetramethylammonium and cesium salts of diplatinum(II) complexes composed of mono-lacunary α-Keggin- and α2-Dawson-type polyoxotungstates, [(CH3)4N]4H[α-AlW11O39{cis-Pt(NH3)2}2]⋅11H2O (TMA-AlW11-Pt-NH3), [(CH3)4N]4H[α-BW11O39{cis-Pt(NH3)2}2]⋅9H2O (TMA-BW11-Pt-NH3), Cs4[α-GeW11O39{Pt(bpy)}2]⋅10H2O (bpy = 2,2′-bipyridine; Cs-GeW11-Pt-bpy), Cs3.5H0.5[α-GeW11O39{Pt(phen)}2]⋅3H2O (phen = 1,10-phenanthroline; Cs-GeW11-Pt-phen), and Cs6[α2-P2W17O61{cis-Pt(NH3)2}2]⋅13H2O (Cs-P2W17-Pt-NH3), were synthesized and characterized by X-ray crystallography, elemental analysis, TG/DTA, FTIR, and solution {1H and 31P} NMR spectroscopy. The characterization results showed that the two platinum(II) moieties, [cis-Pt(NH3)2]2+, [Pt(bpy)]2+, and [Pt(phen)]2+, were coordinated to the mono-vacant site of [XW11O39](12−n)− (Xn+ = Al3+, B3+, and Ge4+) and [α2-P2W17O61]10−. When the eight platinum(II) compounds, [(CH3)4N]3[α-PW11O39{cis-Pt(NH3)2}2]⋅10H2O (TMA-PW11-Pt-NH3), [(CH3)4N]4[α-SiW11O39{cis-Pt(NH3)2}2]·13H2O (TMA-SiW11-Pt-NH3), [(CH3)4N]4[α-GeW11O39{cis-Pt(NH3)2}2]·11H2O (TMA-GeW11-Pt-NH3), TMA-AlW11-Pt-NH3, TMA-BW11-Pt-NH3, Cs-GeW11-Pt-bpy, Cs-GeW11-Pt-phen, and Cs-P2W17-Pt-NH3 were used as photocatalysts for hydrogen evolution from aqueous triethanolamine (TEOA) solution under the light irradiation, Cs-P2W17-Pt-NH3 exhibited the highest activities among the eight diplatinum(II) compounds.

High-Throughput and Sensitive Fluorimetric Strategy for MicroRNAs in Blood Using Wettable Microwells Array and Silver Nanoclusters with Red Fluorescence Enhanced by Metal Organic Frameworks.

A high-throughput and sensitive fluorimetric analysis method has been developed with wettable microwells array for probing short-chain microRNAs (miRNAs) in blood using silver nanoclusters (AgNCs) with red fluorescence amplified and stabilized by metal organic frameworks (MOFs). Glass slides were first spotted with polyacrylic acid to form hydrophilic microdots and then patterned with hydrophobic hexadecyltrimethoxysilane, followed by etching the microdots to yield the microwells array. Furthermore, the DNA capture probes with silver-binding G sequences were covalently bound onto the functionalized microwells to hybridize with targeting miRNAs. Exonuclease I catalytic digestion was then conducted to remove any single-strand DNA probes unhybridized. Eventually, AgNCs were applied to specifically recognize the G sequences of DNA probes survived to be further coated with MOFs of zeolitic imidazolate framework (ZIF-8). Unexpectedly, the red fluorescence of AgNCs probes could be dramatically enhanced due to the "electron-donor effect" of nitrogen-containing ligands of ZIF-8 coatings, together with improved sensing stability. High detection sensitivity and reproducibility could thereby be expected for detecting miRNAs in the blood with the concentrations linearly ranging from 0.175 to 500 pM. Markedly different from the common sandwiched DNA detection methods, the developed fluorimetric strategy using AgNCs coated with MOFs and DNA probes designed with silver-recognizing sequences would be tailored for quantifying various kinds of short-chain miRNAs with low levels in the complicated blood media.